Process for treating sand



May 8, 1934. J. A. CREW PROCESS FOR TREATING SAND Filed DSG. 5l. 1931will! Lua@ kv vmw NEN im owmuwmwi n Y W gwen/coz JA-Crew Patented May 8,1934 UNITED STATES PATENT OFFICE 7 Claims.

This invention relatesto an improved process for treating silica sandsfor the purpose of obtaining in an economical and eiiicient manner,unusually highly purified and decolorized sand which is readily adaptedfor use, among other elds, in the ceramic and glass manufacturingindustries.

It has been proposed heretofore to leach natural sands to removeimpurities or other undesired compounds therefrom of a discoloringcharacter by intimately mixing such natural sands with dilute sulphuricacid and then passing the sand through a heating zone possessing atemperature suliiciently high to evaporate the moisture or water contentof the sand to leave the grains of the latter coated with concentratedsulphuric acid, whereby to permit the sulphuric acid to react with ironoxide compounds contained in the sand so that When the latter is nallywashed or scrubbed, the impurities will be removed with the sulphuricacid, leaving the sand in a purified and bleached state. I have observedthat when the sand is thus treated and is placed in the heating zone andotherwise handled,v it is necessary to employ special corrosionresisting materials since the dilute sulphuric acid readily attacksordinary metals to produce damaging corrosion.

llt is an object of the present invention to provide a process whereinthe sand is first heated to a relatively dry state and to a temperatureabove the boiling point of Water immediately prior to the step of addinga reagent usually in the form of an acid solution to the sand, for thepurpose of assisting in the spreading of the acid over the whole surfaceof each grain by capillarity and surface tension, providing a mucheasier and surer operation than the replacement of water by, forexample, dilute sulphuric acid through diffusion, as is required in theformer method of soaking the same in a bath or vat containing dilutesulphuric acid. Again, my improved process avoids entirely thetransportation of the sand when mixed with dilute sulphuric acidsolutions. Since concentrated sulphuric acid, when applied in the formof a thin lm on the sand grains, is not highly corrosive, it may behandled by ordinary conveyor mechanism of standard design withoutpremature destruction of metal parts through corrosion.

For a further understanding of the invention, reference is to be had tothe following descrip tion and the accompanying drawing, wherein:

Fig. 1 is a diagrammatic view in side elevation disclosing apparatusemployed in carrying the present invention into effect;

Fig. 2 is a horizontal sectional view on the line 2-2 of Fig. 1;

Fig. 3 is a vertical transverse sectional view on 60 the line 3 3 ofFig. 1, disclosing the inlet portion of the mixer; and

Fig. 4 is a chart disclosing the sequence of operations used in carryingout the present invention.

My process is practiced by first taking natural sand and bringing thesame down to grain size, cleaning oli as much as possible of includedimpure matter by customary treating operations. I then take the sand andpass the same through an unlined rotary drier of the type indicated at1, wherein heat is passed through the drier from a suitable heatgenerator in a direction countercurrent to the passage of the sandthrough the drier. This operation serves to greatly reduce the normalmoisture content of the sand and heats it to a desired operatingtemperature, normally, 400 F. which is sufficient to drive 01T allappreciablemoisture. However, the temperature of the heated sand mayvary between 200 F. to whatever upward limit is considered desirable.

Following this initial heating of the sand in the drier 1, I immediatelytransfer, through a belt or other convenient means, the heated sand to abrick lined mixer, indicated at 2. This mixer may be of approximatelythe same form, only shorter than the drier 1, in that it involves arotating drum set on a slight angle with respect to the horizontal. Thedrum of the mixer is indicated at 3 and the interior of the drum ispreferably brick lined and may be provided with lifters 4 by whichturbulence is imparted to the sand as the drum 3 rotates. The drum 3 mayor may not be additionally heated, usually the 'sensible heat of thesand is sufficient to carry 95 out my operation. A pipe line 5 ismounted in the stationary end wall 6 of the drum 3 adjacent to the pointof entrance of the heated sand into said drinn, and the pipe lineterminates in a closed end provided with radial 100 ports 7 by which thesulphuric acid solution or other reagent is introduced into said drumand into contact with the heated sand. This reagent may consist ofsulpiiuric acid or other suitable chemicals in varying proportions. Whenthe acid 105 solution strikes the sand, steam is liberated in copiousquantities and is preferably immediately withdrawn from the mixer by wayof an outlet conduit 8 connected with the stationary end wall 6, theconduit being equipped with a suction fan 110 present in the drier.

or its equivalent 9 whereby to eifect a positive withdrawal of the steamalmost immediately upon its liberation.

Since the sand, prior to its delivery to the mixing drum, is in asubstantially dry and heated state before the reagent is added, theresult is to secure the spreading of the reagent over the whole surfaceof the sand grains, this being assisted by capillarity and surfacetension, enabling the reagent to enter the fine crevices of sand grainand thoroughly coat the surface of each grain with a film of thereagent. This film, in effect, comprises a highly concentrated form ofthe reagent since the water content of the solution is quicklyevaporated and almost instantaneously removed by the operation of thesuction fan in withdrawing the steam from the mixer drum.

This lm of concentrated reagent readily reacts on the surface impuritiesof the sand such as the iron oxide compounds. Since reagents such asconcentrated sulphin'ic acid when in 111m form on the sand grains do notreadily attack metal, the sand upon discharge from the mixer may bereadily handled in ordinary conveying apparatus without involving theuse of special corrosion resisting materials.

Upon discharge from the mixer, the acid coated sand, which ispractically dry to the touch, is transferred by means of a conveyor 10of standard construction to a bin 1l, in which the sand is permitted tostand for a period of several hours in order toY insure thoroughandcomplete reaction between impurities in the sand and the sulphuricacid. Following the retention of the sand within the' bin for a desiredperiod of time, the sand is then transferred to one of a plurality ofscrubbers 12. Water is percolated upwardly through the sand contained ineach scrubber to Wash away the sulphuric acid and the impuritiescombined therewith, the percolation continuing until the liquiddischarged from the top of each bin is negative to acid tests.

If desired, the sands may be again washed with a caustic if an extremelywhite appearance is desired. After being washed to a negative acidcondition, the sand will be flushed to a drag washer and conveyed to adrain b in, thence to a standaid steam drier and finally subjected to agrinding mill operation, whereby it is reduced to its desired state ofiineness.

The advantages resulting from this method of operation have been setforth above but, in addition, it may be pointed out that it permits ofthe employment of an unlined drier, as at 1, whereby to provide forquick firing and good temperature control for the succeeding mixingstep. Preferably, the sand introduced into the drier will bepreliminarily treated by standard apparatus so that it does not possessa moisture content materially in excess of 5 to 6%. 'This moisturecontent consists of water only, no acid being Since no acid is presentwhen the sand is being heated in the drier, there is no likelihood ofdecomposition of the sulphates or the darkening of the sand. By havingthe sand in a dry heated condition when brought into contact with thedilute sulphuric acid solution, the sand grains readily take up thesulphuric acidf'present to provide over each grain of sand a film ordeposit of concentrated sulphuric acid, since the water in the solutionis practically instantly driven off or evaporated in the form of steamand removed from the mixer by way of the outlet conduit 8. This conduitas well as the fan may be formed from corrosion resisting materials ifnecessary.

I prefer to employ the bin 11 whereby to secure the desired period oftime to effect complete reaction between the acid and the sandimpurities although, of course, there are certain operations whereinthisA bin may be omitted since I have found that the reaction is morethan complete by the time the sand is discharged from the mixer.Thorough washing of the sand and removal of acid and impurities can beeffected by the upward percolation of water through the sand deliveredto the scrubbers l2. The temperatures specified are subject to variationand a considerable degree of control both in the drier 1 and the mixer2. Ordinarily, in the drier, the sand is heated to a temperature ofsubstantially 370 F. to 430 F. and is then removed from the drier. Atthe time of introduction into the mixer, the sand may possess atemperature of approximately 350 F., which is well above the boilingpoint oi water so that the lieat stored in the sand may be used to driveoff the water content of a dilute acid solution.

The conditions which exist in the drum 3 and the reactions desired maybe readily controlled by governing the strength of the acid solution, byvarying the rate of feed of the sand into the drier and/or by varyingthe temperature of the sand when introduced into the drum. Lifters 4 insaid drum serve to stir the same and effect its intimate contact withthe acid. By the explosive action of the evolved steam at the feed endof the mixer, a very thorough agitation or turbulence of the sand isobtained, the steam expands rapidly with a considerable degree ofviolence so that an effective intermixture takes place between the sandand the acid reagent. While in the bin 11, the sand may be maintained ata temperature varying between 160 F. and 230 F. and may be held at thistemperature for several hours before washing.

What is claimed is:

1. The process of treating sand, which comprises heating sand to adrying temperature, introducing into the dry sand while the latter is ina heated state an acid reagent in aqueous solution, whereby the heat ofthe sand serves to evaporate substantially the water content of thereagent leaving the grains of the sand covered by the reagent in ahighly concentrated form, withdrawing water vapor from the .sandsubstantially immediately upon its evolution by contact with the heatedsand, and then following the desired period of reaction betveen theconcentrated reagent and the sand, -.ibjecting the sand to a washingaction to remove the reagent and impurities combined therewith.

2. The process of treating sand which comprises heating the sand in theabsence of an acid to a drying temperature in excess of 200 F., thenintroducing into the sand while the latter is in a heated state andduring agitation thereof an aqueous solution of sulphuric acid, andsubstantially immediately removing the liberated water vapor to producea lm of concentrated sulphuric acid on the sand particles.

3. The method of treating sand to remove impurities therefromwhich-consists in continuously passing a body of sand through a heateddrying zone wherein the sand attains a temperature in excess of 200 F.,passing the sand while in a, heated state from the drying zone to amixing zoneand continuously passing the same in an agitated statethrough said zone, and in- Y 'et troducing into contact with the sandduring its passage through the mixing zone an aqueous acid solution,whereby to coat the sand particles with an acid iilm of a concentratedcharacter, the liquid carrier medium of the acid being quickly liberatedas a vapor by initial contact with the heated sand.

4. The method of treating sand to remove impurities therefrom whichconsists in reducing the sand to a substantially dry state by continuouspassage through a drier wherein said sand is heated in the absence of anacid to a temperature of from between 200 F. to 500 F., continuallyremoving the heated sand from the drier and immediately transferring thesame to a mixer through which the sand is continuously passed andagitated, introducing into the mixer an aqueous solution of sulphuricacid, whereby to coat the sand grains with a film composed of a highlyconcentrated solution of sulphuric acid, the liquid carrier agent beingsubstantially'immediately vaporized by the temperature of the sand andremoved from the drier, and then water washing the acid coated sand,following removal from said mixer to remove the acid and combinedimpurities from the treated sand. l

5. The method of treating sand to remove impurities therefrom whichconsists in reducing the sand to a substantially dry state by continuouspassage through a drier wherein said sand is heated in the absence of anacid to a temperature of from between 200 F. to 500 F., continuallyremoving the heated sand from the drier and immediately transferring thesame to a mixer through which the sand is continuously passed andagitated, introducinginto the mixer a weak aqueous solution of sulphuricacid, whereby to coat the sand grains with a film composed of a highlyconcentrated solution of sulphuric acid, the liquid carrier agent beingvaporized by 'the temperature of the sand and removed from the drier,maintaining the f said film on the sand grains for a desired period oftime to secure chemicalvreaction between the sulphuric acid and the ironoxide content of the sand, and then water washing the acid coated sand,following removal from said mixer to remove the acid and combinedimpurities from the treated sand.`

6. In a process of treating sands'to remove ferrous impurities, thesteps which comprise heating the same under substantially atmosphericpressure conditions to a temperature above 200 F. in the absence of anacid, and then introducing into the sand while the latter is in theheated state specified an acid in aqueous solution, the temperature ofthe sand and the presence of normal pressures thereon eifecting asubstantially immediate evaporation of the water content of said acidsolution, and immediately removing the liberated water vapor at the timeof its formation to produce on the sand grains a. film of acid in aconcentrated form.

7. In a process of treating silica sand to remove ferrous impurities,the steps which comprise preheating the sand in the absence of an acid,and then introducing into the sand a quantity of sulphuric acid toproduce on the sand grains a film of acid in concentrated form.

JOSHUA A. CREW.

